This application is based upon and claims the benefit of priority from the prior Japanese Patent Applications No. 2001-050272, filed Feb. 26, 2001; and No. 2002-005151, filed Jan. 11, 2002 the entire contents of both of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a silver halide emulsion and a silver halide photographic light-sensitive material using the same. More particularly, the invention relates to a silver halide emulsion that contains thin grains, exhibits high sensitivity, hard gradation and excellent pressure characteristic.
2. Description of the Related Art
In recent years, photographic emulsions comprising silver halide tabular grains have become to be used widely for the purpose of improving the sensitivity/graininess ratio of silver halide photographic light-sensitive emulsions. Recently, for the purpose of a further improvement in the sensitivity/graininess ratio, there is a tendency that the grain thickness of silver halide tabular grains becomes smaller and the area of main planes becomes larger. This tendency is based on the idea to enhance the photoabsorption to improve the sensitivity/graininess ratio by the adsorption of a large amount of a spectral sensitizing dye caused by the increase of the surface area of silver halide grains per unit volume. This idea is described in U.S. Pat. No. 4,956,269 and so on.
On the other hand, the silver halide composition distribution of silver halide grains is an important factor on which the performance of a silver halide emulsion depends. For a silver iodobromide emulsion or a silver chloroiodobromide emulsion, what is particularly important is in what portion of a silver halide grain and in how much content iodide is distributed. Many patent applications about this subject have been published. Examples thereof include silver halide grains having therein a multilayered structure comprising a plurality of portions differing in iodide content, disclosed in Jpn. Pat. Appln. KOKAI Publication No. (hereinafter referred to as JP-A-) 60-143331 and so on, and silver halide grains which contains iodide in a high content in their surfaces, disclosed in JP-A-63-106745 and so on. These techniques are believed to contribute to the enhancement of sensitivity, pressure characteristic and so on through prevention of photoelectrons and positive holes from their recombination and improvement of developability and optimum control of the adsorption condition of sensitizing dye.
Further, a technology to enhance sensitivity and pressure characteristic by locally forming a phase with a high iodide content during the formation of silver halide grains is widely used in this technical field. Particularly, the technology to intentionally introduce dislocation lines into silver halide grains by locally forming phases with a high iodide content has been studied in the art. JP-A-63-220238 discloses a method for introducing a dislocation line to a peripheral portion of a silver halide tabular grain. JP-A-1-102547 discloses a method for introducing a dislocation line in a main plane of a silver halide tabular grain.
In the fields of silver iodobromide emulsions and silver chloroiodobromide emulsions, using iodide as described above has become a practical technique. On the other hand, however, it has been pointed out that the degree of uniformity of iodide content between grains of silver halide easily has an effect on photographic properties of silver halide emulsions containing iodide. Some patent applications about this fact, for example, JP-A""s-2-256043 and 11-15089, have been published.
These patent applications disclose that the enhancement of uniformity of iodide content between silver halide grains can improve photographic properties of silver halide emulsions.
Moreover, patent applications that focus uniformity of microscopic distribution of iodide in a silver halide grain have also been published.
WO89/06830 discloses a technique relating to silver halide grains having a silver iodobromide phase the halogen composition of which is so uniform that no fluctuation or no ununiformity of halogen composition can be detected by observation using a transmission electron microscope. JP-A-11-125874 discloses that making the variation coefficient of intergrain iodide distribution in portions near grain surfaces to be 45% or less can improve photographic properties such as sensitivity.
The known patent applications and so on relating to the uniformity of iodide distribution between or in silver halide grains, however, investigate no silver halide emulsion comprising thin tabular grains having a thickness of 0.1 xcexcm or less.
As described above, it is true that the reduction of grain thickness results in the increase of surface area per unit volume to enhance photoabsorption.
However, in the region where the grain thickness is 0.1 xcexcm or less, there is a fact that no enhancement occurs in sensitivity/graininess ratio corresponding to the increase of photoabsorption. This fact occurs more notably in the case where a main plane has an equivalent-circle diameter of 3.0 xcexcm or more. Only insufficient investigation has been made for silver halide tabular grains having a grain thickness of 0.1 xcexcm or less about what type of uniformity of intergrain or intragrain iodide distribution is desirable. There are expectations for further increase in sensitivity/graininess ratio of silver halide emulsions through the development of technologies focusing on the aforementioned point.
It is an object of the present invention to increase the sensitivity/graininess ratio of emulsions comprising silver halide tabular grains through providing emulsions comprising silver halide tabular grains having uniformity of intergrain and intragrain iodide distributions suitable for the cases where the grain thickness is 0.1 xcexcm or less. Another object of the present invention is to reduce the change of photographic properties occurring when a pressure is applied. Still another object of the present invention is to provide silver halide emulsions having higher sensitivities by the above means.
After the intensive investigations by the inventors of the present invention, the objects of the present invention have attained using the following silver halide emulsions and silver halide light-sensitive materials:
(1) A silver halide emulsion comprising silver halide grains, wherein the variation coefficient of equivalent-circle diameters of all the silver halide grains is 40% or less, and 70% or more of the total projected area of all the grains is accounted for by silver halide grains each satisfying the following requirements (i), (ii) and (iii):
(i) a silver iodobromide or silver iodochlorobromide tabular grain having (111) planes as main planes thereof,
(ii) a thickness thereof is 0.1 xcexcm or less, and
(iii) surface iodide contents in the main plain thereof meeting the following relations:
Io less than 30 mol % and
0.7Io less than Is less than 1.3Io
wherein xe2x80x9cIsxe2x80x9d is an average value of surface iodide contents (Ip""s) in the main plane of each grain and xe2x80x9cIoxe2x80x9d is an average value of the xe2x80x9cIsxe2x80x9d values of all the tabular grains;
(2) The silver halide emulsion recited in item (1) above, wherein each of the silver halide tabular grains accounting for 70% or more of the total projected area further satisfying requirement (iv) below:
(iv) the equivalent-circle diameter is 1.0 xcexcm or more, and the variation coefficient of the distribution of the surface iodide contents (Ip""s) in one silver halide grain is 30% or less, wherein the surface iodide content being measured in every measurement area all over the main plane of the silver halide grain and the measurement area being a square having a side length of 100 nm;
(3) The silver halide emulsion recited in item (1) or (2) above, wherein in the requirement (iii) above, the average value of surface iodide contents in the main plane of each grain represented by xe2x80x9cIsxe2x80x9d satisfies the relation: 0.8Io less than Is less than 1.2Io;
(4) The silver halide emulsion recited in item (2) or (3) above, wherein in the requirement (iv) above, the variation coefficient of the surface iodide contents in a silver halide grain represented by xe2x80x9cIp""sxe2x80x9d is 20% or less;
(5) The silver halide emulsion recited in item (1), wherein each of the silver halide tabular grains accounting for 70% or more of the total projected area further satisfying requirement (ivxe2x80x2) below:
(ivxe2x80x2) the equivalent-circle diameter is 3.0 xcexcm or more;
(6) The silver halide emulsion recited in any one of items (2) to (4) above, wherein in the requirement (iv) above, the equivalent-circle diameter is 3.0 xcexcm or more;
(7) The silver halide emulsion recited in any one of items (1) to (6) above, wherein when the emulsion is irradiated with an electromagnetic wave of 325 nm under the environment of an absolute temperature of 6xc2x0 K., induced fluorescence of 575 nm with an intensity of at least one third the intensity of the maximum fluorescent emission induced in the wavelength range of from 490 to 560 nm, is emitted;
(8) The silver halide emulsion recited in any one of items (1) to (7) above, wherein each of the silver halide tabular grains accounting for 70% or more of the total projected area further satisfying requirement (v) below:
(v) when the distribution of iodide contents is measured on an imaginary plane inside the tabular grain which is parallel to the main plane and which is present in the depth of 20% of the tabular grain thickness from the main plane, the measurement points at which the iodide content is maximum distribute in the form of a circle surrounding the center of the imaginary plane, wherein the iodide content being measured in every measurement area all over the imaginary plane and the measurement area being a square having a side length of 100 nm;
(9) The silver halide emulsion recited in item (8) above, wherein the iodide contents at the measurement points at which the iodide contents are maximum are within the range of from 15 mol % to 40 mol %;
(10) The silver halide emulsion recited in any one of items (1) to (9) above, wherein each of the silver halide tabular grains accounting for 70% or more of the total projected area further having 10 or more dislocation lines per grain at the peripheral portion thereof; and
(11) A silver halide photographic light-sensitive material, wherein a light-sensitive emulsion layer contains the silver halide emulsion recited in any one of items (1) to (10) above.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.